The present invention relates to production of explosives.
In current practice, primary explosive for priming of explosive devices (e.g. ammunition cartridges and detonators) is prepared away from the priming zone in a large batch or at the maximum possible continuous rate. At the priming stage, explosive is drawn from store and mixed with other ingredients of a composition in a substantial batch which is then distributed between elements of the devices (e.g. cap shells, cartridge cases or detonator cases). This sequence involves bulk storage, transport to a mixing station, the mixing operation itself, transport of the mixture to the priming zone, and distribution between said elements. Since primary explosives are inherently dangerous to manufacture and handle, each stage of the sequence is hazardous and needs special precautions, particularly where explosive is present in bulk.
In a method of producing explosive for priming explosive devices, the present invention employs any one of the following three features alone, or any combination of them:
(1) said explosive is produced in a relatively small quantity, preferably appropriate to an individual utilisation demand,
(2) said explosive is produced at a relatively low output rate, preferably not substantially greater than the rate at which it is used in priming,
(3) production of said explosive is substantially continuous, or simultaneous, with its further utilisation.
The explosive may be produced in a batch sufficient for a plurality of individual utilisation demands, but small relative to conventional batches. In order to satisfy total output demand, there may be a series of such batches, which can be separated by a distance and/or in a manner facilitating isolation of an explosion in any one batch. The batches can be produced in regular succession, e.g. at predetermined time intervals, thereby facilitating adequate spacing and subsequent handling.
The maximum permissible size of each batch will depend upon the type of explosive and the conditions under which it has to be produced. The sensitivity, explosive energy, required production conditions and divisibility for use of the explosive will affect the batch size. The total output demand per unit time will also influence the batch size, as will the precautions taken to isolate individual batches. Conventional priming composition for rimfire cartridges uses lead styphnate as primary explosive: a batch of styphnate sufficient for, say, 20 priming charges for rimfire cartridges could be made and divided between the rimfire cases in a continuous operation: corresponding arrangements could be made for priming shotgun cap shells and detonator cases. Larger batches will obviously involve extra precautions, but batches as large as several ounces could be produced at intervals of about one minute.
Batches may also be combined for an individual utilisation demand, or for total output demand if not immediately used. However, neither combination nor division of batches is preferred, since both incur additional hazards. The preferred arrangement is one in which a batch is matched to an individual utilisation demand, for example each batch in a series is just sufficient for a priming charge for one rimfire cartridge, shotgun cap or detonator. This permits simultaneous production and utilisation where the explosive is produced in situ in a utilising device.
In this specification, the terms "utilising device" and "production in situ" have the following meanings:
Utilising device--refers to a combination of at least two elements of an explosive device, at least one of which elements is a body of said explosive. The other element may be a mere container or carrier for the explosive, such as a rimfire cartridge case, a detonator case or a cap shell. The utilising device may be a finished explosive device, but it is more likely to be only partly finished; for example (a) further elements may have to be added to it to make up the explosive device, such as propellant and a bullet for a rimfire cartridge, or an electric match or a fuse for a detonator; (b) the elements may have to be reshaped, or relocated relative to each other as when priming composition in a rimfire cartridge case is forced into the rim of the case by a conventional spinning punch after explosive has formed in the head of the case.
Production in situ--means that the explosive is produced in relation to at least one other element so as to provide said combination. Where the other element is a container, the explosive will normally be produced within it. If the other element were a carrier, the explosive could be produced as a body around a portion of the carrier. As indicated above, producing in situ does not imply that the combination is immediately ready for final use.
The explosive may be produced in a continuous or semi-continuous stream but at a rate which is low relative to conventional continuous or semi-continuous processes.
Production of explosive in the form of a continuous stream or series of batches is facilitated if the production process is continuous, or simultaneous, with the utilisation stage, for example incorporation in an explosive device. Continuity does not imply immediate use; in practice, there will inevitably be a degree of "live storage" where production is not effected in situ. However, there will be a continuous flow path between the production and utilisation stages, so that off-line storage of dangerous substances is reduced or eliminated. To this end, the production rate and utilisation rate are preferably substantially matched, at least on average over a period.
In any process according to the invention, the components used to produce the explosive are preferably comparatively insensitive, thereby mitigating storage problems.
A production process in accordance with the invention is preferably automated. The components required for production of the explosive may be automatically metered into batches under controlled thermal conditions, even where small quantities are required. Preferably, too, an automated production process is integrated with an automated utilisation stage producing at least a partially finished explosive device; for example, in the case of rimfire cartridge priming, primary explosive production can be continuous with an automatic line for receiving primed cases, loading propellant, and inserting the bullet.